1. Field of the Invention
The present invention relates to a liquid injector for injecting a liquid into a subject, and more particularly to a liquid injector for injecting a liquid into a subject who is to be imaged by an imaging diagnostic apparatus such as a CT (Computed Tomography) apparatus, an MRI (Magnetic Resonance Imaging) apparatus, an angiography apparatus, or the like.
2. Description of the Related Art
Presently available imaging diagnostic apparatus for capturing fluoroscopic images of subjects include CT scanners, MRI apparatus, PET (Positron Emission Tomography) apparatus, ultrasonic diagnostic apparatus, angiography apparatus, MRA (MR Angiography) apparatus, and ultrasonograph.
When such an imaging diagnostic apparatus is used to capture a fluoroscopic image of a subject, it is occasionally practiced to inject a liquid such as a contrast medium or a saline solution into the subject. There has been put to practical use a liquid injector for automatically injecting a liquid into a subject. Such a liquid injector has a drive motor and a slider mechanism, and employs a liquid syringe that is removably mounted.
The liquid syringe comprises a cylinder and a piston slidably inserted in the cylinder. The cylinder is filled with a liquid such as a contrast medium or a saline solution to be injected into the subject. The liquid syringe is connected to the subject by an extension tube and set on a liquid injection mechanism. The liquid injection mechanism individually holds the piston and the cylinder and moves them relatively to each other for injecting a liquid, typically a contrast medium, from the liquid syringe into the subject.
The operator determines the rate at which the contrast medium is to be injected and the total amount of the contrast medium to be injected, in view of various conditions, and then enters data representing the rate and total amount into the liquid injection mechanism. Based on the entered data, the liquid injection mechanism injects the contrast medium into the subject. The injected contrast medium changes the image contrast of the subject, allowing the imaging diagnostic apparatus to capture a good fluoroscopic image of the subject.
Some liquid injectors are capable of injecting a saline solution as well as a contrast medium into the subject. For operating such a liquid injector, the operator enters, if desired, an instruction to inject the saline solution following the completion of the injection of the contrast medium, together with data representing the rate at which the saline solution is to be injected and the total amount of the saline solution to be injected, into the liquid injector.
Based on the entered data, the liquid injector first injects the contrast medium and then automatically injects the saline solution after the contrast medium has been injected. The subsequently injected saline solution pushes the previously injected contrast medium, reducing the consumption of the contrast medium, and also reduces artifacts in the captured image.
Liquid injectors of the type described above have been devised and applied for patent by the applicant of the present application (see, for example, patent documents 1, 2 below).    Patent document 1: Japanese laid-open patent publication No. 2002-11096;    Patent document 2: Japanese laid-open patent publication No. 2002-102343.
The above liquid injector is capable of injecting a contrast medium into the subject in order to change the image contrast of the subject to a state which allows the imaging diagnostic apparatus to capture a good fluoroscopic image of the subject.
For injecting an appropriate amount of contrast medium at an appropriate rate into the subject, the operator is required to determine the rate at which the contrast medium is to be injected and the total amount of the contrast medium to be injected, in view of various conditions including an area to be imaged of the subject and the weight of the subject, and enter numerical data representing the rate and the total amount into the liquid injector. This process is too complex for unskilled operators to carry out easily, and does not prevent inappropriate numerical values to be entered into the liquid injector.
In particular, since a plurality of different types of contrast mediums containing effective components which have different concentrations are now available on the market, the operator needs to determine and enter the rate at which the contrast medium is to be injected and the total amount of the contrast medium to be injected, also in view of the type of the contrast medium to be used. This situation makes the entire data entry process more complex, and poses an increased burden on the operator in determining and entering the above data for both a contrast medium and a saline solution if the operator is operating a liquid injector which is capable of injecting both the contrast medium and the saline solution.